Dr. Smith: Are we *sure* Ebola isn’t airborne?

Since yesterday’s post, several people have asked me on various social media outlets about the airborne nature of Ebola. Didn’t I know about this paper (“Transmission of Ebola virus from pigs to non-human primates“), which clearly showed that Ebola could go airborne?

Indeed I do–I wrote about that paper two years ago, and it in no way changes my assertion that Ebola doesn’t spread between people in an airborne manner.

Let me back up. The paper in question was an experimental study done in the wake of the 2008 finding of the Reston Ebola virus in pigs and a previous study looking at the Zaire virus in pigs. In the air transmission study, they inoculated pigs with Ebola and examined transmission to macaques (who were not in direct contact with the infected pigs).

They did find aerosolized Ebola in air samples, and some of the macaques did come down with symptoms of Ebola. So, it looked like pigs could spread Ebola through the air, which is something that had already been suggested by the epidemiology of the 2008 pig Ebola outbreak. It’s always nice when experimental data matches up with that observed during a real-life occurrence of the virus.

*However*, the kicker was not that Ebola is transmitted by air in human outbreaks, but rather that there may be something unique about pig physiology that allows them to generate more infectious aerosols as a general rule–so though aerosols aren’t a transmission route between primates (including humans, as well as non-human primates used experimentally), pigs may be a bigger threat as far as aerosols. Thus, this may be important for transmission of swine influenza and other viruses as well as Ebola.

I've just finished re-reading Richard Preston's 1995 book The Hot Zone, which deals largely with a 1989 Ebola outbreak in Reston, Virginia, among Philippine crabeater monkeys imported for medical research.

A key factor in the outbreak was that it was indeed airborne: the virus moved from one room to another in the building where the monkeys were kept caged. An Army team was able, with great difficulty, to enter the building, euthanize the monkeys, and take samples. One result was the identification of a new strain, Ebola Reston.

One of the most striking results of this very alarming event was that four employees in the building housing the monkeys were eventually found to be carrying Ebola Reston antibodies. But the same airborne strain that killed the monkeys had no symptomatic effect on the humans.

So far, then, we've been absurdly lucky: We can sicken and die from strains of Ebola (like Zaire) that aren't airborne, but something about the airborne strains can't do us serious harm.

A "counterfactual" airborne Ebola epidemic, breaking out in the Washington, DC area in the winter of 1989-90, would have had a catastrophic effect on the US and the world. The last quarter-century would have been dramatically different.

Since yesterday’s post, several people have asked me on various social media outlets about the airborne nature of Ebola. Didn’t I know about this paper (“Transmission of Ebola virus from pigs to non-human primates“), which clearly showed that Ebola could go airborne?

Indeed I do–I wrote about that paper two years ago, and it in no way changes my assertion that Ebola doesn’t spread between people in an airborne manner.

Let me back up. The paper in question was an experimental study done in the wake of the 2008 finding of the Reston Ebola virus in pigs and a previous study looking at the Zaire virus in pigs. In the air transmission study, they inoculated pigs with Ebola and examined transmission to macaques (who were not in direct contact with the infected pigs).

They did find aerosolized Ebola in air samples, and some of the macaques did come down with symptoms of Ebola. So, it looked like pigs could spread Ebola through the air, which is something that had already been suggested by the epidemiology of the 2008 pig Ebola outbreak. It’s always nice when experimental data matches up with that observed during a real-life occurrence of the virus.

*However*, the kicker was not that Ebola is transmitted by air in human outbreaks, but rather that there may be something unique about pig physiology that allows them to generate more infectious aerosols as a general rule–so though aerosols aren’t a transmission route between primates (including humans, as well as non-human primates used experimentally), pigs may be a bigger threat as far as aerosols. Thus, this may be important for transmission of swine influenza and other viruses as well as Ebola.

I've just finished re-reading Richard Preston's 1995 book The Hot Zone, which deals largely with a 1989 Ebola outbreak in Reston, Virginia, among Philippine crabeater monkeys imported for medical research.

A key factor in the outbreak was that it was indeed airborne: the virus moved from one room to another in the building where the monkeys were kept caged. An Army team was able, with great difficulty, to enter the building, euthanize the monkeys, and take samples. One result was the identification of a new strain, Ebola Reston.

One of the most striking results of this very alarming event was that four employees in the building housing the monkeys were eventually found to be carrying Ebola Reston antibodies. But the same airborne strain that killed the monkeys had no symptomatic effect on the humans.

So far, then, we've been absurdly lucky: We can sicken and die from strains of Ebola (like Zaire) that aren't airborne, but something about the airborne strains can't do us serious harm.

A "counterfactual" airborne Ebola epidemic, breaking out in the Washington, DC area in the winter of 1989-90, would have had a catastrophic effect on the US and the world. The last quarter-century would have been dramatically different.